Differential uplift and tilt of Pleistocene reef platforms and Quaternary slip rate on the Morne-Piton normal fault (Guadeloupe, French West Indies)

[1] The Guadeloupe islands are cut by normal faults that accommodate oblique convergence between the North American and Caribbean plates. Such faults are responsible for part of the shallow seismicity and have produced M ≥ 5 damaging earthquakes. To better assess the seismic hazard in Guadeloupe, we quantify the slip rate on one of the largest fault (Morne-Piton). This roughly E-W fault crosses the island of Marie-Galante and uplifts a flight of reef terraces. From geomorphic analysis, we mapped three main terraces. New U/Th datings show that they formed during the latest interglacials, ∼120 and ∼240 kyr ago. Correlation with SPECMAP isotopic records implies that the Marie-Galante plateau emerged during the ∼330 ka highstand. Topographic profiles show that the terraces and the plateau are deformed by faulting. Elastic modeling of their shape constrains the geometry of the fault (70–80° dip, 5 km depth) and its slip rate (0.5 ± 0.2 mm/yr). Given its length (50 km), depth, and slip rate, this fault might produce maximum M ∼ 6.5 earthquakes with a recurrence time of 1400 to 3300 years, or more likely smaller events such as the M ∼ 5.5 16 May 1851 and 3 August 1992 shocks that might recur every 400 to 1000 years. We also show that all the islands and terraces are tilted westward perpendicularly to the trench. La Desirade closest to the trench is uplifted by 276 m, whereas subsidence (−70 m) is observed 10 km east of the volcanic arc. This tilt probably resulted from a transient deformation episode at the subduction interface that predated the late Pleistocene.